应选择密度已知的置换液，其中待测材料不溶，且在真空下具有良好的润湿性和较低的蒸发率。高沸点芳香烃或脂肪族烃是合适的。进行测定时的温度t会影响置换液的密度；每次称重应在恒定温度下进行。其原理是在皮重管中称量一定量的干燥样品，用置换液润湿，离心，直到堵塞的空气被清除，并根据质量差计算密度。

Displacement liquids of known density should be selected in which the material to be tested is insoluble, and which has good wetting properties and a low evaporation rate under vacuum. High-boiling aromatic or aliphatic hydrocarbons are suitable. The temperature, t, at which the determination is carried out affects the density of the displacement liquid; each weighing should be made at a constant temperature. The principle consists in weighing into a tared tube a quantity of a dried sample, wetting it with displacement liquid, centrifuging until the occluded air is removed and calculation of the density from the difference of masses.